The present disclosure relates to a reactive power compensator and a method of controlling the same.
With the development of industry and the increase in population, a power demand rapidly increases, but there is a limitation in power production.
Therefore, a power system for stably supplying power generated in a production area to a consumer without loss is becoming increasingly more important.
There is a need for a flexible AC transmission system (FACTS) for improving a power flow, a system voltage, and stability. A static synchronous compensator (STATCOM) of the FACTS, which is called a third generation power compensator, is connected in parallel to a power system to compensate for reactive power required by the power system.
FIG. 1 is a diagram illustrating a general power system 10.
As shown in FIG. 1, the general power system 10 may include a power generation source 20, a power system 30, a load 40, and a plurality of reactive power compensators 50.
The power generation source 20 may mean a place or a facility which generates power. The power generation source 20 may be understood as a power producer.
The power system 30 may mean a whole facility including a power line, a steel tower, an arrester, an insulator, and the like, which transmits the power generated in the power generation source 20 to the load 40.
The load 40 may mean a place or a facility which consumes the power generated in the power generation source 20. The load 40 may be understood as a consumer who consumes power.
The reactive power compensators 50 are the STATCOM and are a device that is connected to the power system 30 to compensate for reactive power when the reactive power of power flowing into the power system 30 is low.
The reactive power compensators 50 each include a converter which converts AC power of the power system 30 into DC power or converts DC power into AC power.
The converter includes a cluster with respect to each of three phases, and three phase clusters each including a plurality of cells connected in series to one another.
FIG. 2A is a circuit diagram of a converter having a star connection topology, and FIG. 2B is a circuit diagram of a converter having a delta connection topology.
As shown in FIGS. 2A and 2B, a plurality of cells 54 are connected in series to each of the three phase clusters 52.
In the case of both a converter having a star connection and a converter having a delta connection, in order to secure reliability and excellent operation performance, uniform energy (voltage) control is important between clusters and uniform voltage control is important between cells in each cluster.
In order for the uniform energy control between the clusters, the converter having the star connection uses a zero sequence voltage, and the converter having the delta connection uses a zero sequence current.
An existing uniform control method using a zero sequence voltage has limitations in that control is impossible and a calculation is complicated when a current is not supplied.
In addition, an existing uniform control method using a zero sequence current has limitations in that reliability of uniform control is lowered because a negative sequence component is not considered.